public static String toString_2(int[] arr){
	StringBufffer sb = new StringBuffer();
	sb.append("[");
	for(int i = 0; i < arr.length;i++){
		if(i!=arr.length-1){
			sb.append(arr[i]+",");
		}else{
			sb.append(arr[i]+"]");
		}
	}
	return sb.toString();
}